package secretSharing;

import java.util.Arrays;
import java.util.Random;

public class ThresholdSecretSharing {
    // private static Logger LOG = Logger.getLogger(ThresholdSecretSharing.class.getName());
    public final static int MAX_SECRET_BYTES = 65536;
    public final static int MAX_SHARES = 255;
    private static int[] EXP_OP = { 0x01, 0x03, 0x05, 0x0f, 0x11, 0x33, 0x55, 0xff, 0x1a, 0x2e, 0x72, 0x96, 0xa1, 0xf8, 0x13, 0x35, 0x5f, 0xe1, 0x38, 0x48,
            0xd8, 0x73, 0x95, 0xa4, 0xf7, 0x02, 0x06, 0x0a, 0x1e, 0x22, 0x66, 0xaa, 0xe5, 0x34, 0x5c, 0xe4, 0x37, 0x59, 0xeb, 0x26, 0x6a, 0xbe, 0xd9, 0x70,
            0x90, 0xab, 0xe6, 0x31, 0x53, 0xf5, 0x04, 0x0c, 0x14, 0x3c, 0x44, 0xcc, 0x4f, 0xd1, 0x68, 0xb8, 0xd3, 0x6e, 0xb2, 0xcd, 0x4c, 0xd4, 0x67, 0xa9,
            0xe0, 0x3b, 0x4d, 0xd7, 0x62, 0xa6, 0xf1, 0x08, 0x18, 0x28, 0x78, 0x88, 0x83, 0x9e, 0xb9, 0xd0, 0x6b, 0xbd, 0xdc, 0x7f, 0x81, 0x98, 0xb3, 0xce,
            0x49, 0xdb, 0x76, 0x9a, 0xb5, 0xc4, 0x57, 0xf9, 0x10, 0x30, 0x50, 0xf0, 0x0b, 0x1d, 0x27, 0x69, 0xbb, 0xd6, 0x61, 0xa3, 0xfe, 0x19, 0x2b, 0x7d,
            0x87, 0x92, 0xad, 0xec, 0x2f, 0x71, 0x93, 0xae, 0xe9, 0x20, 0x60, 0xa0, 0xfb, 0x16, 0x3a, 0x4e, 0xd2, 0x6d, 0xb7, 0xc2, 0x5d, 0xe7, 0x32, 0x56,
            0xfa, 0x15, 0x3f, 0x41, 0xc3, 0x5e, 0xe2, 0x3d, 0x47, 0xc9, 0x40, 0xc0, 0x5b, 0xed, 0x2c, 0x74, 0x9c, 0xbf, 0xda, 0x75, 0x9f, 0xba, 0xd5, 0x64,
            0xac, 0xef, 0x2a, 0x7e, 0x82, 0x9d, 0xbc, 0xdf, 0x7a, 0x8e, 0x89, 0x80, 0x9b, 0xb6, 0xc1, 0x58, 0xe8, 0x23, 0x65, 0xaf, 0xea, 0x25, 0x6f, 0xb1,
            0xc8, 0x43, 0xc5, 0x54, 0xfc, 0x1f, 0x21, 0x63, 0xa5, 0xf4, 0x07, 0x09, 0x1b, 0x2d, 0x77, 0x99, 0xb0, 0xcb, 0x46, 0xca, 0x45, 0xcf, 0x4a, 0xde,
            0x79, 0x8b, 0x86, 0x91, 0xa8, 0xe3, 0x3e, 0x42, 0xc6, 0x51, 0xf3, 0x0e, 0x12, 0x36, 0x5a, 0xee, 0x29, 0x7b, 0x8d, 0x8c, 0x8f, 0x8a, 0x85, 0x94,
            0xa7, 0xf2, 0x0d, 0x17, 0x39, 0x4b, 0xdd, 0x7c, 0x84, 0x97, 0xa2, 0xfd, 0x1c, 0x24, 0x6c, 0xb4, 0xc7, 0x52, 0xf6, 0x01, 0x03, 0x05, 0x0f, 0x11,
            0x33, 0x55, 0xff, 0x1a, 0x2e, 0x72, 0x96, 0xa1, 0xf8, 0x13, 0x35, 0x5f, 0xe1, 0x38, 0x48, 0xd8, 0x73, 0x95, 0xa4, 0xf7, 0x02, 0x06, 0x0a, 0x1e,
            0x22, 0x66, 0xaa, 0xe5, 0x34, 0x5c, 0xe4, 0x37, 0x59, 0xeb, 0x26, 0x6a, 0xbe, 0xd9, 0x70, 0x90, 0xab, 0xe6, 0x31, 0x53, 0xf5, 0x04, 0x0c, 0x14,
            0x3c, 0x44, 0xcc, 0x4f, 0xd1, 0x68, 0xb8, 0xd3, 0x6e, 0xb2, 0xcd, 0x4c, 0xd4, 0x67, 0xa9, 0xe0, 0x3b, 0x4d, 0xd7, 0x62, 0xa6, 0xf1, 0x08, 0x18,
            0x28, 0x78, 0x88, 0x83, 0x9e, 0xb9, 0xd0, 0x6b, 0xbd, 0xdc, 0x7f, 0x81, 0x98, 0xb3, 0xce, 0x49, 0xdb, 0x76, 0x9a, 0xb5, 0xc4, 0x57, 0xf9, 0x10,
            0x30, 0x50, 0xf0, 0x0b, 0x1d, 0x27, 0x69, 0xbb, 0xd6, 0x61, 0xa3, 0xfe, 0x19, 0x2b, 0x7d, 0x87, 0x92, 0xad, 0xec, 0x2f, 0x71, 0x93, 0xae, 0xe9,
            0x20, 0x60, 0xa0, 0xfb, 0x16, 0x3a, 0x4e, 0xd2, 0x6d, 0xb7, 0xc2, 0x5d, 0xe7, 0x32, 0x56, 0xfa, 0x15, 0x3f, 0x41, 0xc3, 0x5e, 0xe2, 0x3d, 0x47,
            0xc9, 0x40, 0xc0, 0x5b, 0xed, 0x2c, 0x74, 0x9c, 0xbf, 0xda, 0x75, 0x9f, 0xba, 0xd5, 0x64, 0xac, 0xef, 0x2a, 0x7e, 0x82, 0x9d, 0xbc, 0xdf, 0x7a,
            0x8e, 0x89, 0x80, 0x9b, 0xb6, 0xc1, 0x58, 0xe8, 0x23, 0x65, 0xaf, 0xea, 0x25, 0x6f, 0xb1, 0xc8, 0x43, 0xc5, 0x54, 0xfc, 0x1f, 0x21, 0x63, 0xa5,
            0xf4, 0x07, 0x09, 0x1b, 0x2d, 0x77, 0x99, 0xb0, 0xcb, 0x46, 0xca, 0x45, 0xcf, 0x4a, 0xde, 0x79, 0x8b, 0x86, 0x91, 0xa8, 0xe3, 0x3e, 0x42, 0xc6,
            0x51, 0xf3, 0x0e, 0x12, 0x36, 0x5a, 0xee, 0x29, 0x7b, 0x8d, 0x8c, 0x8f, 0x8a, 0x85, 0x94, 0xa7, 0xf2, 0x0d, 0x17, 0x39, 0x4b, 0xdd, 0x7c, 0x84,
            0x97, 0xa2, 0xfd, 0x1c, 0x24, 0x6c, 0xb4, 0xc7, 0x52, 0xf6 };
    private static int[] LOG_OP = { 0x00, 0x00, 0x19, 0x01, 0x32, 0x02, 0x1a, 0xc6, 0x4b, 0xc7, 0x1b, 0x68, 0x33, 0xee, 0xdf, 0x03, 0x64, 0x04, 0xe0, 0x0e,
            0x34, 0x8d, 0x81, 0xef, 0x4c, 0x71, 0x08, 0xc8, 0xf8, 0x69, 0x1c, 0xc1, 0x7d, 0xc2, 0x1d, 0xb5, 0xf9, 0xb9, 0x27, 0x6a, 0x4d, 0xe4, 0xa6, 0x72,
            0x9a, 0xc9, 0x09, 0x78, 0x65, 0x2f, 0x8a, 0x05, 0x21, 0x0f, 0xe1, 0x24, 0x12, 0xf0, 0x82, 0x45, 0x35, 0x93, 0xda, 0x8e, 0x96, 0x8f, 0xdb, 0xbd,
            0x36, 0xd0, 0xce, 0x94, 0x13, 0x5c, 0xd2, 0xf1, 0x40, 0x46, 0x83, 0x38, 0x66, 0xdd, 0xfd, 0x30, 0xbf, 0x06, 0x8b, 0x62, 0xb3, 0x25, 0xe2, 0x98,
            0x22, 0x88, 0x91, 0x10, 0x7e, 0x6e, 0x48, 0xc3, 0xa3, 0xb6, 0x1e, 0x42, 0x3a, 0x6b, 0x28, 0x54, 0xfa, 0x85, 0x3d, 0xba, 0x2b, 0x79, 0x0a, 0x15,
            0x9b, 0x9f, 0x5e, 0xca, 0x4e, 0xd4, 0xac, 0xe5, 0xf3, 0x73, 0xa7, 0x57, 0xaf, 0x58, 0xa8, 0x50, 0xf4, 0xea, 0xd6, 0x74, 0x4f, 0xae, 0xe9, 0xd5,
            0xe7, 0xe6, 0xad, 0xe8, 0x2c, 0xd7, 0x75, 0x7a, 0xeb, 0x16, 0x0b, 0xf5, 0x59, 0xcb, 0x5f, 0xb0, 0x9c, 0xa9, 0x51, 0xa0, 0x7f, 0x0c, 0xf6, 0x6f,
            0x17, 0xc4, 0x49, 0xec, 0xd8, 0x43, 0x1f, 0x2d, 0xa4, 0x76, 0x7b, 0xb7, 0xcc, 0xbb, 0x3e, 0x5a, 0xfb, 0x60, 0xb1, 0x86, 0x3b, 0x52, 0xa1, 0x6c,
            0xaa, 0x55, 0x29, 0x9d, 0x97, 0xb2, 0x87, 0x90, 0x61, 0xbe, 0xdc, 0xfc, 0xbc, 0x95, 0xcf, 0xcd, 0x37, 0x3f, 0x5b, 0xd1, 0x53, 0x39, 0x84, 0x3c,
            0x41, 0xa2, 0x6d, 0x47, 0x14, 0x2a, 0x9e, 0x5d, 0x56, 0xf2, 0xd3, 0xab, 0x44, 0x11, 0x92, 0xd9, 0x23, 0x20, 0x2e, 0x89, 0xb4, 0x7c, 0xb8, 0x26,
            0x77, 0x99, 0xe3, 0xa5, 0x67, 0x4a, 0xed, 0xde, 0xc5, 0x31, 0xfe, 0x18, 0x0d, 0x63, 0x8c, 0x80, 0xc0, 0xf7, 0x70, 0x07 };

    private int add(int a, int b) {
        return a ^ b;
    }

    private int mul(int x, int y) {
        if (x == 0 || y == 0)
            return 0;
        int v = LOG_OP[0xff & x] + LOG_OP[0xff & y];
        assert v >= 0 && v < 512;
        return EXP_OP[v];
    }

    private int div(int x, int y) {
        if (x == 0)
            return 0;
        if (y == 0)
            throw new IllegalArgumentException("division by 0");
        int v = 0xff + LOG_OP[0xff & x] - LOG_OP[0xff & y];
        assert v >= 0 && v < 512;
        return EXP_OP[v];
    }

    /**
     * Generate a set of shares from the secret provided. Secret reconstruction will require 'threshold' shares in order to reconstruct correctly a secret
     *
     * @param secret
     *            byte array of len 1..65536
     * @param shares
     *            number of shares to generate
     * @param threshold
     *            number of required shares in order to reconstruct a secret
     * @param rnd
     *            Source for random numbers (this must be a good random number generator)
     * @return byte array of byte arrays (a list of shares as raw bytes)
     */
    public byte[][] createShares(byte[] secret, int shares, int threshold, Random rnd) {
        if (secret == null)
            throw new IllegalArgumentException("null secret");
        int m = secret.length;
        if (m == 0)
            throw new IllegalArgumentException("invalid secret length: 0");
        if (m > MAX_SECRET_BYTES)
            throw new IllegalArgumentException("invalid secret length: " + m + "(gt " + MAX_SECRET_BYTES + " bytes)");
        if (shares < 1)
            throw new IllegalArgumentException("not enought shares: " + shares);
        if (shares > MAX_SHARES)
            throw new IllegalArgumentException("too many shares: " + shares + "(gt" + MAX_SHARES + ")");
        if (threshold > shares)
            throw new IllegalArgumentException("threshold > shares: " + threshold + " > " + shares);
        byte[][] share = new byte[shares][m + 1];
        for (int i = 0; i < shares; i++)
            share[i][0] = (byte) (i + 1);

        byte[] a = null;
        try {
            a = new byte[threshold];
            for (int i = 0; i < m; i++) {
                rnd.nextBytes(a);
                a[0] = secret[i];
                for (int j = 0; j < shares; j++)
                    share[j][i + 1] = (byte) eval(share[j][0], a);
            }
        } finally {
            if (a != null)
                Arrays.fill(a, (byte) 0);
        }
        return share;
    }

    private int eval(byte x, byte[] a) {
        assert x != 0;
        assert a.length > 0;
        int r = 0;
        int xi = 1;
        for (byte b : a) {
            r = add(r, mul(b, xi));
            xi = mul(xi, x);
        }
        return r;
    }

    /**
     * Reconstructs a secret from a list of raw bytes shares
     *
     * @param shares
     *            byte array of byte arrays (a list of shares as raw bytes)
     * @return recovered byte array secret
     */
    public byte[] recoverSecret(byte[]... shares) {
        if (shares == null)
            throw new IllegalArgumentException("null shares");

        int threshold = shares.length;
        if (threshold == 0)
            throw new IllegalArgumentException("not enought shares:" + threshold);
        if (threshold > MAX_SHARES)
            throw new IllegalArgumentException("too many shares:" + threshold);
        int m = shares[0].length - 1;
        if (m <= 0)
            throw new IllegalArgumentException("invalid share length:" + (m + 1) + " (<=0)");
        if (m > MAX_SECRET_BYTES)
            throw new IllegalArgumentException("invalid share length:" + (m + 1) + " (>" + (MAX_SECRET_BYTES + 1) + ")");

        for (int i = 1; i < shares.length; i++) {
            if (shares[i] == null)
                throw new IllegalArgumentException("share " + i + " is null");
            if (shares[i].length != m + 1)
                throw new IllegalArgumentException("shares are not equal length, inconsistent input");

        }
        byte[] u = null;
        byte[] v = null;
        try {
            u = new byte[threshold];
            for (int i = 0; i < threshold; i++) {
                u[i] = shares[i][0];
                if ((0xff & u[i]) == 0)
                    throw new IllegalArgumentException("invalid share index: " + shares[i][0]);
                for (int j = 0; j < i; j++)
                    if (u[i] == u[j])
                        throw new IllegalArgumentException("duplicated share index: " + u[i]);

            }
            byte[] secret = new byte[m];
            v = new byte[threshold];
            for (int j = 0; j < m; j++) {
                for (int i = 0; i < threshold; i++)
                    v[i] = shares[i][j + 1];
                secret[j] = (byte) lagrange(u, v);
            }
            return secret;
        } finally {
            if (u != null)
                Arrays.fill(u, (byte) 0);
            if (v != null)
                Arrays.fill(v, (byte) 0);
        }
    }

    private int poly(int i, byte[] u) {
        int r = 1;
        for (int j = 0, m = u.length; j < m; j++)
            if (j != i)
                r = mul(r, div(u[j], add(u[j], u[i])));
        return r;
    }

    private int lagrange(byte[] u, byte[] v) {
        int m = u.length;
        assert m == v.length;
        int r = 0;
        for (int i = 0; i < m; i++)
            r = add(r, mul(poly(i, u), v[i]));
        return r;
    }

}